1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus having a polishing section for polishing a workpiece such as a semiconductor wafer to a flat mirror finish and a cleaning section for cleaning the workpiece which has been polished.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 xcexcm wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. An abrasive cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the abrasive cloth and clamped between the top ring and the turntable. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the abrasive cloth is therefore polished to a flat mirror finish while the top ring and the turntable are rotating.
Further, in the polishing apparatus, abrasive slurry is supplied from a nozzle onto the abrasive cloth attached to the upper surface of the turntable. The abrasive slurry contains abrasive material such as silicon dioxide (SiO2) or cerium dioxide (CeO2) having a diameter of 1 xcexcm or less in a liquid. The abrasive slurry contains water, abrasive material, and a small amount of dispersing agent to prevent aggregation of the abrasive material. Further, in order to perform chemical polishing in addition to mechanical polishing, acid or alkali may be added to the abrasive slurry.
The surface of the semiconductor wafer which has been polished is generally quite contaminated not only with particles of semiconductor material but also with abrasive material. The count of contaminants on the surface of the semiconductor wafer may be as high as 100,000 particles per wafer, and it is required to reduce this count to about 100 particles per wafer by some efficient method.
The conventional polishing apparatus could not be placed in a clean room because of dust particles generated by the polishing apparatus itself. Once the contaminants which adhere to the surface of the polished semiconductor wafer have been dried, it is difficult to remove the contaminants by cleaning. Therefore, the present practice is to preserve the semiconductor wafers which have been polished in water, immediately after polishing, in a specially constructed water-containing carrier which is brought into the clean room so that the semiconductor wafers may be cleaned in a cleaning device.
However, in the conventional apparatus, the cleaning device is spaced from the polishing apparatus and the semiconductor wafers must be transferred from the polishing apparatus to the cleaning device in such a state that they are preserved in water, thus productivity of the semiconductor wafers are lowered. Further, because the cleaning device itself becomes quite polluted from the dust particles adhering to the semiconductor wafers, it is not possible to use general cleaning devices provided in the clean room. That is, a special cleaning machine must be provided for exclusively cleaning the semiconductor wafers which have been polished. This leads to high apparatus cost.
It is therefore an object of the present invention to provide a polishing apparatus which can be installed in a clean room and does not contaminate the ambient atmosphere in the clean room, and which can polish, clean and dry workpieces such as semiconductor wafers so that the workpieces can be discharged to a next processing station by using regular carriers available generally in the clean room.
Another object of the present invention is to provide a polishing apparatus which can prevent particulate contamination originating in polishing activities so that the polishing apparatus can be installed in a clean room.
According to one aspect of the present invention, there is provided a polishing apparatus for polishing a surface of a workpiece comprising: a housing unit; a partition wall partitioning an interior of the housing unit into a first chamber and a second chamber, the partition wall having a first opening for allowing the workpiece to pass therethrough; a polishing section having a turntable with an abrasive cloth mounted on an upper surface thereof and a top ring positioned above the turntable for supporting the workpiece to be polished and pressing the workpiece against the abrasive cloth, the polishing section being disposed in the first chamber; a cleaning section for cleaning the workpiece which has been polished, the cleaning section being disposed in the second chamber; a transferring device for transferring the workpiece which has been polished from the polishing section to the cleaning section through the first opening; and exhaust means for exhausting ambient air from each of the polishing section and the cleaning section separately and independently.
According to the polishing apparatus presented above, the polishing section and the cleaning section are housed in the housing unit, and the two sections are isolated from each other by the partition wall. Therefore, the entire polishing apparatus can be disposed in a clean room without contaminating the clean room atmosphere. The semiconductor wafers can be polished and cleaned within the polishing apparatus, and transferred to the next processing stations using regular carriers available in the clean room generally. The two sections of the polishing apparatus are separated by the partition wall having the opening which is closed with a shutter, and the ambient atmospheres in the polishing section and the cleaning section are exhausted separately and independently. This arrangement prevents any dust particles such as mist of abrasive slurry and ground-off material generated during a polishing operation from contaminating the clean room by either maintaining the polishing section at a pressure lower than the cleaning section or by closing a shutter which is provided for the opening of the partition wall.
According to another aspect of the present invention, there is provided a polishing apparatus for polishing a surface of a workpiece comprising: a housing unit; a partition wall partitioning an interior of the housing unit into a first chamber and a second chamber, the partition wall having a first opening for allowing the workpiece to pass therethrough; a polishing section having a turntable with an abrasive cloth mounted on an upper surface thereof and a top ring positioned above the turntable for supporting the workpiece to be polished and pressing the workpiece against the abrasive cloth, the polishing section being disposed in said first chamber; a cleaning section for cleaning the workpiece which has been polished, the cleaning section being disposed in the second chamber; a transferring device for transferring the workpiece which has been polished from the polishing section to the cleaning section through the first opening; and exhaust means for exhausting ambient air from each of the polishing section and the cleaning section; wherein the cleaning section comprises a cleaning unit for cleaning the workpiece while supplying cleaning solvent and a drying unit for drying the workpiece which has been cleaned.
According to the polishing apparatus presented above, a workpiece such as a semiconductor wafer is polished in the polishing section, the workpiece which has been polished is transferred from the polishing section to the cleaning section, and then the workpiece is cleaned and dried in the cleaning section. Therefore, the workpiece is discharged from the polishing apparatus in such a state that the workpiece is clean and dry.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.